Along with miniaturization of a semiconductor device, the trend is moving into a shorter wavelength of the exposure light source and a higher numerical aperture (higher NA) of the projection lens, and a so-called immersion method of filling a high refractive-index liquid (hereinafter sometimes referred to as an “immersion liquid”) between the projection lens and the sample with an attempt to raise the resolution by more shortening the wavelength is known. The immersion method is effective for all pattern profiles and furthermore, can be combined with the super-resolution technology under study at present, such as phase-shift method and modified illumination method.
Since the advent of a resist for KrF excimer laser (248 nm), an image forming method called chemical amplification is used as an image forming method for a resist so as to compensate for sensitivity reduction caused by light absorption. For example, the image forming method by positive chemical amplification is an image forming method of decomposing an acid generator in the exposed area upon exposure to produce an acid, converting an alkali-insoluble group into an alkali-soluble group by using the generated acid as a reaction catalyst in the baking after exposure (PEB: Post Exposure Bake), and removing the exposed area by alkali development.
The resist for ArF excimer laser (193 nm) using this chemical amplification mechanism is predominating at present, but when the resist is immersion-exposed, a pattern collapse problem of causing collapse of the formed line pattern to give rise to a defect at the production of a device is involved, or the performance in terms of LWR (line width roughness) of the pattern side wall being roughened is not satisfied yet.
Also, it is pointed out that when the chemical amplification resist is applied to immersion exposure, the resist layer comes into contact with the immersion liquid at the exposure and the resist layer deteriorates or a component adversely affecting the immersion liquid bleeds out from the resist layer. To solve this problem, in JP-A-2006-309245 (the term “JP-A” as used herein means, an “unexamined published Japanese patent application”), JP-A-2007-304537, JP-A-2007-182488 and JP-A-2007-153982, there is described a case of preventing the bleed-out by adding a resin containing a silicon atom or a fluorine atom.
Furthermore, in the immersion exposure process, when the exposure is performed using a scanning-type immersion exposure machine, unless the immersion liquid moves following the movement of the lens, the exposure speed decreases and this may affect the productivity. In the case where the immersion liquid is water, the resist film is preferably hydrophobic because of good followability of water.
In addition, even when immersion exposure is performed using the above-described technique, it is demanded to more reduce a development defect called Blob defect or generation of a sum.
Various compounds have been also found for the acid generator that is a main constituent component of the chemical amplification resist composition, and a compound capable of decomposing upon irradiation with an actinic ray to generate a sulfonic acid is being generally used. Furthermore, various studies are made also on the cation structure of the acid generator, and an acid generator having naphthylsulfonium cation or phenylsulfonium cation is disclosed, for example, in JP-A-10-232490. In addition, an acid generator having a cyclic sulfonium cation is disclosed in JP-A-2003-195489.
However, in view of overall performance as a resist, it is actually very difficult to find out an appropriate combination of a resin, a photo-acid generator, an additive, a solvent and the like used for the resist. In the formation of a fine pattern having as a small line width as 100 nm or less, even when the resolution performance is excellent, the line pattern formed collapses to give rise to a defect at the production of a device, and improvement of pattern collapse is being required.